Dressing tool for forming and dressing helically ribbed grinding wheels

ABSTRACT

The invention provides a dressing tool for and a method of forming and dressing helically ribbed grinding wheels for grinding the tooth flanks of spur gears and other profiles that can be generated by rolling, wherein at least the tooth flanks which form the working surfaces of the dressing tool are provided with diamonds embedded in a matrix, and the addendum of the teeth of the dressing tool is about 1.2 x m and the dedendum is about 1.4 x m, whereas the addendum of a gearwheel that is to be ground is about 1.0 x m and the dedendum is about 1.2 x m, m being the module of the dressing tool and of the gear wheel that is to be ground with the helically ribbed grinding wheel.

United States Patent 2,260,593 l0/l94l lnventor Fritz Bocker 34,Bahnhofstrasse, 4703, Bonen, Westphalia, Germany App]. No. 745,216

Filed July 16, 1968 Patented Aug. 31, 1971 DRESSING TOOL F OR FORMINGAND DRESSING HELICALLY RIBBED GRINDING WHEELS 6 Claims, 5 Drawing Figs.

us. on. 125/11 R, 51/206 P, 51/287 Int. Cl ..B24b 53/06, B24b l/OO Fieldof Search 51/2063, 287; 125/11, 39

References Cited UNITED STATES PATENTS Wittlinger 76/W C 2,776,5291/1957 Osplack l25/l1 X 2,824,556 2/1958 Bateman 125/11 1,759,333 5/1930Wildhaber 51/206 2,482,785 9/1949 Lohutko l25/l1 Primary Examiner-HaroldD. Whitehead Attorney-Markva, Smith 8:. Kruger ABSTRACT: The inventionprovides a dressing tool for and a method of forming and dressinghelically ribbed grinding wheels for grinding the tooth flanks of spurgears and other profiles that can be generated by rolling, wherein atleast the tooth flanks which form the working surfaces of the dressing Itool are provided with diamonds embedded in a matrix, and

the addendum of the teeth of the dressing tool is about 1.2 x m and thededendum is about 1.4 x m, whereas the addendum of a gearwheel that isto be ground is about 1.0 x m and the dedendum is about 1.2 x m, m beingthe module of the dressing tool and of the gear wheel that is to beground with the helically ribbed grinding wheel.

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SHEET 2 BF 2 In van [or FRITZ 56c KER DRESSING TOOL FOR FORMING ANDDRESSING HELICALLY RIBBED GRINDING WHEELS BACKGROUND OF THE INVENTIONThe invention relates to a dressing tool for forming and dressinghelically ribbed grinding wheels for grinding the tooth flanks of spurgears and other profiles that can be generated by rolling such ascycloidal gear teeth or splined shafts.

A known method of grinding the tooth flanks of spur gears consists inusing cylindrical helically ribbed grinding wheels with rack toothprofiles. It is also known that the profile of a helically ribbedgrinding wheel can be dressed with one or more diamonds which cooperatewith the rotating wheel, and which are guided to generate the profilethat is to be dressed. It is also known to form and/or dress helicallyribbed grinding wheels with a diamond on a revolving disc which istraversed across the revolving grinding wheel. lrrespectively as towhether a single point or a gearwheel-shaped dressing tool is used, itssharp cutting edges cooperate with the grinding wheel and detachindividual particles from the surface of the ribs on the wheel.

Forming and/or dressing helically ribbed grinding wheels by thegenerating principle with a single-point tool is intended to acceleratemachining compared with a tool shaped like a gearwheel. However, asingle-point tool'has the defect that it is incapable of producing aconstant pitch thread on the wheel because it generates a different,namely a smaller, pitch on the major diameter than on the minor diameterof the helical rib. This is due to the fact that during the infeed ofthe profiled tooth towards the wheel that is to be dressed, theone-sided cutting thrust acting on the tooth causes the latter as wellas the gear train to be elastically deflected contrary to the directionof rotation, said deflection being in the opposite direction when thetooth is withdrawn from the work. This circumstance modifies the pitchof the helical gearwheel that is being dressed in an undesirable manner,resulting in faulty work because only the outer portions of the ribs ofsuch grinding wheels actually grind.

On the other hand, when the profile is formed with the cutting edges ofa steel wheel errors on the surface of the grinding wheel are producedby back lash in the same way as during hobbing. Moreover, a forming anddressing process using a steel wheel can be performed only at a speedwhich is considerably lower than the grinding speed.

SUMMARY OF THE INVENTION In order to avoid the shortcomings ofconventional dressing processes, the present invention proposes toprovide a dressing tool in the form of a spur gear for the productionand dressing of helically ribbed grinding wheels for grinding the toothflanks of spur gears and other profiles that can be generated byrolling, wherein at east the tooth flanks which form the workingsurfaces of the dressing tool are provided with diamonds embedded in amatrix.

In such a tool, contrary to conventional tools in which the edges havethe machining action, it is the tooth flanks that act on the ribs of thegrinding wheel. The position of the dressing tool in relation to theribbed grinding wheel is the same as that between the ribbed grindingwheel and the gearwheel that is to be ground. Since the forces acting onthe operative tooth flanks are symmetrical, lateral deflection, as inthe case of a single-point tool, cannot occur. Since edges are notinvolved in the dressing action there is also no back lash. The surfaceof the helically ribbed grinding wheel therefore remains free fromirregularities due to the presence of back lash. The dressing of apreshaped helically ribbed grinding wheel and the formation of theprofiles in a grinding wheel blank can be performed at the same speed asthat conventional in grinding processes based on the generatingprinciple. Compared with conventional tools the proposed tool thereforehas a considerably longer life and the dressing or forming time is verymuch reduced.

During the entire forming and dressing operation the driving gear trainis evenly loaded and the adverse effect of backlash between the wheelsof the gear train and of elastic flexure in the coupling between thework and the workholding spindle when the load varies and the torque isreversed are therefore absent. Consequently the proposed tool permitshelically ribbed grinding wheels which have a very precisely pitchedthread to be produced. Such wheels will then'ensure high accuracy in thegeneration of the tooth flanks on the gearwheels they grind. At the sametime any possible error in individual flanks of the dressing wheel canbe corrected by the corresponding flanks of the following tooth, and thehelically ribbed grinding wheel will therefore be better shaped anddressed than could have been expected from the action of a single toothflank of the dressing tool. The greater accuracy of its helical ribsincidentally improves the working life of the grinding wheel. Since theproposed dressing tool has an effect on the grinding wheel whichresembles the machining action of grinding, the grinding wheel is alsomore accurate than a grinding wheel that has been trued and dressed bythe removal of particles with a sharp cutting edge.

In order to permit the dressing tool to be produced as cheaply aspossible, the diamonds or particles of diamond grit are preferablystatistically, i.e. randomly, distributed over the tooth flanks. Thisnaturally means that their distribution on consecutive tooth flanksfacing the same way will be different. A random distribution and theconsequent overlap in the action of the diamonds reduces the roughnessof the surface of the grinding wheel which is therefore capable ofgrinding a high quality surface on gear wheels. The gear trainscontaining such gear wheels will run exceptionally smoothly.

In an alternative embodiment of the invention, particularly in dressingtools which have a small number of teeth, it is proposed to distributethe diamonds on the tooth flanks in a geometrically defined patterninstead of in random distribution and in such a way that the pattern isstaggered on each consecutive tooth flank in relation to the precedingtooth flank facing the same way. This distribution makes for economy inthe use of the diamonds.

According to another feature of the invention it is proposed to providethe bottom of the space between consecutive teeth as well as the crestsof the teeth of the dressing tool with diamonds and also to make theaddendum of the teeth of the dressing tool as well as the dedendumgreater than in the gear wheel the dressed grinding wheel is intended togrind. When the helically ribbed grinding wheel has been dressed by thedressing tool the base circle can be corrected with a diamond armeddisc. Experience has shown that in a suitable dimensional relationshipthe addendum of the teeth of the dressing tool may be about 1.2Xm andthe dedendum about l.4 m if the addendum of the gearwheel that is to beground is about 1.0Xm and the dedendum about 1.2Xm, m being the moduleof the dressing tool and of the gearwheel that is to be ground with thedressed grinding wheel. For reasons that will be explained thesedimensions provide considerable advantages over conventional dressingtools and methods of dressing helically ribbed grinding wheels.

If the dressing tool is a gearwheel which by virtue of the greateraddendum and dedendum circles of its teeth is about 1.5 mm. smaller atthe roots and about 0.5 mm. larger at the crests-corresponding to amodule of m=2.5 mm.than a normal gearwheel that is to be ground with thedressed helically ribbed wheel, then the ribs on this wheel will beground to a greater depth than would actually be necessary and thisensures that the wheel will abrade only the blanks of the gear teeththat are to be ground. The above-mentioned deviations therefore have theadvantage that the crests of the teeth and the bottom of the spacebetween the teeth of the ground work will not be included in thegrinding action. The ground gearwheel will not therefore be machined inthose areas which are not directly in mating contact in use. Besidesthis fact the arrangement and the method proposed by the presentinvention have the further advantage that the helically ribbed grindingwheel will not itself be as highly loaded as would be the case if thedepth of the threads were not in excess of what would strictly benecessary.

Furthermore, wear of the dressing tool has a diminished effect upon theaccuracy of the gearwheel that is to be ground.

The helically ribbed grinding wheel is preferably dressed at exactly thesame speed as that used for grinding the gearwheel. If the dressing toolis axially reciprocated across the wheel as when dressing the grindingwheel of a plain grinding machine-the grain of the helically ribbedwheel will be cut and not broken out as is the case in conventionalgenerating tools. Another useful circumstance is that owing to the largenumber of diamond chips that are present these are not highly stressed.

It has already been pointed out that the proposed dressing tool issuitable for dressing helically ribbed grinding wheels of any desiredprofile, for instance including globoidal wheels with cycloidal ribbing,and of forming such tools during production.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention will behereinafter more particularly described with reference to theaccompanying drawings in which:

FIG. 1 is a side view of a dressing tool according to the invention withstraight axial teeth mating with a helically ribbed grinding wheel;

FIG. 2 is a perspective top plan view of the arrangement according toFIG. 1;

FIG. 3 is a top plan view of a dressing tool with helical teeth matingwith a helically ribbed grinding wheel;

FIG. 4 is a fragmentary perspective view, on an enlarged scale, of adressing tool containing diamonds in random distribution, and

FIG. 5 is a fragmentary view of a dressing tool with diamonds arrangedin a geometrically defined pattern.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 and 2 show a dressingtool 1 which has the form of a gear wheel with straight axial gearteeth. Diamonds 2 are embedded in the tooth profiles, i.e. in the toothflanks as well as in the bottom and the crests between the flanks ofthis gearwheel. As will be understood by reference to FIG. 2 thesediamonds 2 are distributed in the tooth flanks in a geometricallydefined pattern consisting of parallel rows 3. The position of the rows3 of diamonds 2 on consecutive tooth flanks 5 and 5 facing the same waydiffers inasmuch as the rows 3 are relatively staggered so that there isconsiderable overlap in the action of the diamonds when the dressingtool 11 is in opera- U011.

The teeth of the dressing tool 1 engage the ribs of a helically ribbedgrinding wheel 4 which has the form of a globoidal helix. This grindingwheel 4 which is mounted on a shaft 6 revolves together with the drexingtool 1 at a speed which corresponds to that at which a gearwheel notshown in the drawing that is to be ground is rotated. Consequently thetooth flanks of the helically ribbed grinding wheel ,4 will becontinuously ground and trued by the diamonds 2 on the tooth flanks 5and 5, the tooth flanks of several ribs of the grinding wheel 4 andhence several teeth of the grinding wheel 4 being ground at the sametime. The grinding wheel 4 can therefore be rotated at a fairly highspeed and ground with maximum precision, in conformity with the shape ofthe dressing tool 1 to permit the grinding wheel 4 to be subsequentlyused for grinding the tooth flanks of the gearwheel. This effect isfurther improved if the dressing tool I is reciprocated in the directionindicated by the double-headed arrow 20 in FIG. 2.

Substantially the embodiment illustrated FIG. 3 differs from theabove-described embodiment in that the dressing tool 10 has helicallycut gear teeth provided with diamonds 12 which are statisticallydistributed on the tooth flanks 15 and 15, i.e. located in randomdistribution. This embodiment likewise has the advantage of pennittingseveral ribs 17 of a helically ribbed grinding wheel 14 to besimultaneously dressed by the action of the diamonds 12 in the toothflanks l5 and 15.

FIG. 4 shows a dressing tool with straight axial gear teeth and it willbe seen that in this instance not only the tooth flanks 23, 23', 23" and24 are provided with diamonds in random distribution but also the bottom21, 21, 21" of each tooth space and the crests 22, 22', 22" of theteeth.

In the dressing tool 1 in FIG. 5 the addendum a above the pitch circle Tand the dedendum b' exceed the corresponding dimensions a and b of thegearwheel the dressed grinding wheel is intended to grind. These smallerdimensions a and b of the gearwheel, which is not shown, are indicatedin discontinuous lines in FIG. 5.

It will further be clear that in this dressing tool the distribution ofthe diamonds likewise includes the crests 22 of the teeth and thebottoms of the spaces between them, but in this instance thedistribution is not random but geometrically regular in rows which arerelatively staggered on consecutive tooth flanks 23 and 23' facing thesame way.

I claim:

1. A dressing tool in the form of a spur gear for the production anddressing of helically ribbed grinding wheels of the globoidal type forgrinding the tooth flanks of spur gears and other profiles that can begenerated by rolling, wherein the surfaces of the tooth flanks whichform the working surfaces of the dressing tool are provided withdiamonds embedded in a matrix, the distribution of diamonds inconsecutive tooth flanks facing in either direction being different,whereby the roughness of the surface of the helical ribs on the grindingwheel is minimized.

2. A dressing tool according to claim 1, wherein the addendum of theteeth of the dressing tool is about l.2Xm and the dedendum is about1.4Xm, whereas the addendum of a gearwheel that is to be ground is about1.0Xm and the dedendum is about l.2Xm, m being the module of thedressing tool and of the gearwheel that is to be ground with thehelically ribbed grinding wheel 3. A method of producing and dressinghelically ribbed grinding wheels of the globoidal type for grinding thetooth flanks of spur gears and other profiles which can be generated bya rolling action, comprising the steps of:

a. rotating a gearwheellike dressing tool having diamonds embedded inthe surface of its tooth flanks about an axis,

b. meshing the dressing tool teeth with a helically ribbed grindingwheel such that only the planar surfaces of the tooth flanks contact theribs of the grinding wheel, the axis of said grinding wheel beingtransverse to that of said dressing tool, and

c. cutting the grain of the rib surfaces of the helically ribbedgrinding wheel by rotating said grinding wheel and said dressing toolwhereby the surfaces of the tooth flanks of the dressing tool dress theribs of the grinding wheel.

4. A method as claimed in claim 3, wherein the dressing tool is axiallyreciprocated across the helically ribbed grinding wheel during thedressing operation.

5. A method as claimed in claim 3, wherein a dressing tool is used theaddendum of the teeth of which is about l.2Xm and the dedendum of whichis about 1.4Xm in relation to the addendum of about l.0 m and thededendum of about l.2Xm of a gearwheel that is to be ground, m being themodule of the dressing tool and of the gearwheel that is to be groundwith the helically ribbed grinding wheel, and a pertinent root linediameter of the helically ribbed grinding wheel is corrected by means ofa diamonds carrying disc after the dressing of said helically ribbedgrinding wheel.

6. A dressing tool as set forth in claim 1 wherein the diamonds areembedded in the tooth flanks in a geometrically defined pattern ofdistribution, the pattern on each consecutive tooth flank facing ineither direction being located on the tooth flank at a differentposition with respect to the next adjacent tooth flank facing in thesame direction, whereby there is an overlap in the action of thediamonds on each consecutive tooth flank minimizing the roughness of thesurface of the helical ribs on the grinding wheel.

1. A dressing tool in the form of a spur gear for the production anddressing of helically ribbed grinding wheels of the globoidal type forgrinding the tooth flanks of spur gears and other profiles that can begenerated by rolling, wherein the surfaces of the tooth flanks whichform the working surfaces of the dressing tool are provided withdiamonds embedded in a matrix, the distribution of diamonds inconsecutive tooth flanks facing in either direction being different,whereby the roughness of the surface of the helical ribs on the grindingwheel is minimized.
 2. A dressing tool according to claim 1, wherein theaddendum of the teeth of the dressing tool is about 1.2 X m and thededendum is about 1.4 X m, whereas the addendum of a gearwheel that isto be ground is about 1.0 X m and the dedendum is about 1.2 X m, m beingthe module of the dressing tool and of the gearwheel that is to beground with the helically ribbed grinding wheel
 3. A method of producingand dressing helically ribbed grinding wheelS of the globoidal type forgrinding the tooth flanks of spur gears and other profiles which can begenerated by a rolling action, comprising the steps of: a. rotating agearwheellike dressing tool having diamonds embedded in the surface ofits tooth flanks about an axis, b. meshing the dressing tool teeth witha helically ribbed grinding wheel such that only the planar surfaces ofthe tooth flanks contact the ribs of the grinding wheel, the axis ofsaid grinding wheel being transverse to that of said dressing tool, andc. cutting the grain of the rib surfaces of the helically ribbedgrinding wheel by rotating said grinding wheel and said dressing toolwhereby the surfaces of the tooth flanks of the dressing tool dress theribs of the grinding wheel.
 4. A method as claimed in claim 3, whereinthe dressing tool is axially reciprocated across the helically ribbedgrinding wheel during the dressing operation.
 5. A method as claimed inclaim 3, wherein a dressing tool is used the addendum of the teeth ofwhich is about 1.2 X m and the dedendum of which is about 1.4 X m inrelation to the addendum of about 1.0 X m and the dedendum of about 1.2X m of a gearwheel that is to be ground, m being the module of thedressing tool and of the gearwheel that is to be ground with thehelically ribbed grinding wheel, and a pertinent root line diameter ofthe helically ribbed grinding wheel is corrected by means of a diamondscarrying disc after the dressing of said helically ribbed grindingwheel.
 6. A dressing tool as set forth in claim 1 wherein the diamondsare embedded in the tooth flanks in a geometrically defined pattern ofdistribution, the pattern on each consecutive tooth flank facing ineither direction being located on the tooth flank at a differentposition with respect to the next adjacent tooth flank facing in thesame direction, whereby there is an overlap in the action of thediamonds on each consecutive tooth flank minimizing the roughness of thesurface of the helical ribs on the grinding wheel.